Silicon carbide, SiC, is a covalent crystalline material with the diamond structure. It can be produced in block form by the reaction of SiO.sub.2 with carbon within a temperature range of about 1,900.degree.-2,200.degree. C. SiC is generally chemically inert, extremely hard, and has a high thermal conductivity and low thermal expansion. It can be used in a variety of high temperature applications, such as electrical heating units, furnace walls, mufflers, abrasives, rocket nozzles, as well as engine and turbine parts.
In order to produce a silicon carbide product having a particularly defined shape, the above described block can be crushed and cleaned by washing with acid and alkali. The resultant powder can then be molded and sintered to form pressureless or reaction sintered SiC shapes. This method is not readily adapted to forming SiC films or fibers, however.
In an effort to produce SiC films and fibers, organosilicon polymeric materials have been used as ceramic precursors to the fibers. For example, polysilanes (containing R.sub.2 Si and RSi units) and polycarbosilanes (containing R.sub.2 SiCH.sub.2 units) are such preceramic polymers that can be converted into ceramic materials by pyrolysis, i.e., by heating the materials at elevated temperatures. See, for example, R. West et al., Am. Ceram. Soc. Bull., 62, 899 (1983); and S. Yajima in Handbook of Composites; Eds, E. Watt and B.V. Perov; Elsevier, N.Y.; Vol. 1, Ch. VI, pp. 201-37, 1985. More recently, silicon acetylene polymers, which can be cast into films and fibers, have been shown to produce SiC by pyrolysis. See, for example, U.S. Pat. Nos. 4,940,767 (Barton et al., Jul. 10, 1990) and 4,965,332 (Barton et al., Oct. 23, 1990). Multistep preparation and purification processes and/or the presence of large quantities of unwanted by-products, such as salts, have made many of these methods inefficient, costly, and commercially unattractive.
It is a principal object of the present invention, therefore, to provide an organosilicon polymer that can be used directly and conveniently to form ceramic films and fibers. Another object of the present invention is to provide an organosilicon polymer that can undergo thermolysis to SiC. A further object of the invention is to provide an easy, efficient, clean, and fast process for preparing organosilicon polymers, and the subsequent SiC products, in high char yields, i.e., wherein high total yields of the SiC are obtained from the polymer after pyrolysis.